High performance refrigerator having insulated evaporator cover

ABSTRACT

A high performance refrigerator includes a cabinet with a refrigerated interior, an insulating cover separating a portion of the cabinet from the refrigerated interior, and a refrigeration fluid circuit having an evaporator located within the portion of the cabinet separated by the insulating cover from the refrigerated interior. The refrigerator also includes a controller that commands the refrigerator to perform a defrosting cycle when the evaporator coil requires defrosting. This defrosting cycle includes closing dampers in the insulating cover during the defrosting of the evaporator coil, thereby keeping the refrigerated interior thermally isolated from the evaporator during the defrost cycle. The controller is also operable to stop operation of a defrost heater when the evaporator reaches a first target temperature above the freezing point of water, and to re-open the dampers when the evaporator reaches a second target temperature above the freezing point of water.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the priority benefit of U.S. ProvisionalPatent Application No. 61/548,795 (pending), filed Oct. 19, 2011, thedisclosure of which is hereby incorporated by reference in its entiretyherein.

FIELD OF THE INVENTION

The present invention relates generally to refrigerators or freezersand, more particularly, to refrigeration systems for use with highperformance blood bank refrigerators or plasma freezers.

BACKGROUND OF THE INVENTION

Refrigeration systems are known for use with laboratory refrigeratorsand freezers of the type known as “high performance refrigerators,”which are used to cool their interior storage spaces to relative lowtemperatures such as about −30° C. or lower, for example. These highperformance refrigerators are used to store blood and/or plasma, in oneexample.

Known refrigeration systems of this type include a single loopcirculating a refrigerant. The system transfers energy (i.e., heat) fromthe refrigerant to the surrounding environment through a condenser, andthe system transfers heat energy to the refrigerant from the cooledspace (e.g., a cabinet interior) through an evaporator. The refrigerantis selected to vaporize and condense at a selected temperature close tothe desired temperature for the cooled space, such that therefrigeration system can maintain the cooled space near that selectedtemperature during operation.

One common problem with known refrigeration systems is that theevaporator includes coils that tend to produce and accumulate frostalong the outer surface if any moisture is ambient within the cooledspace. If enough frost accumulation occurs, the ability of theevaporator to remove heat from the cooled space is detrimentallyimpacted. Consequently, known refrigeration systems require a defrostcycle where the evaporator coils are heated to remove the frost. Thisdefrost cycle may be a manual defrost or an automatic defrost, but bothtypes of defrost cycles are undesirable for various reasons.

In a manual defrost cycle, all of the products stored in the cabinet areremoved and the cooled space is left exposed to the ambient environmentto heat up the evaporator coils and melt the frost. This cycle isundesirable because the products stored in the cabinet need to be storedin an alternative refrigerator for the duration of the defrost cycle,and also because the melting process can produce a significant amount ofmoisture that needs to be removed from the cabinet. In an automaticdefrost cycle, the evaporator coils are rapidly heated by a localheating unit or hot gas flow to remove the frost, which is collected bya trough and delivered out of the cooled space. The cooled spacenecessarily undergoes a temperature spike during this automatic defrostcycle, which can jeopardize the products stored in the cabinet.

There is a need, therefore, for a refrigerator that substantiallyminimizes or eliminates a temperature spike within the cooled spaceduring a defrost cycle.

SUMMARY OF THE INVENTION

In one embodiment, a refrigerator includes a cabinet with a refrigeratedinterior and a refrigeration fluid circuit for circulating arefrigerant. The refrigeration fluid circuit includes a compressor, acondenser, an expansion device, and an evaporator located within thecabinet. The evaporator includes an evaporator coil, an evaporator fanproducing air flow through the evaporator coil, and a defrost heater.The refrigerator also includes an insulating cover separating a portionof the cabinet containing the evaporator from the refrigerated interior.The insulating cover includes at least one damper which opens to permitair circulation from the refrigerated interior through the evaporator.

The refrigerator further includes a controller operable to command therefrigerator to perform a series of steps defining a defrost cycle whenthe evaporator coil requires defrosting. The series of steps includesstopping operation of the compressor and the evaporator fan, closing theat least one damper to thermally isolate the evaporator from therefrigerated interior, and starting operation of the defrost heater. Therefrigerated interior remains thermally isolated from the evaporatorduring operation of the defrost heater.

In one aspect, the refrigerator also includes a temperature sensor fordetecting the temperature of the evaporator. The controller operatesduring defrosting as follows: when the temperature sensor detects thatthe evaporator has reached a first target temperature above the freezingpoint of water, the defrost heater stops. After any remaining moisturedrips off the evaporator coils, the compressor starts. When thetemperature sensor detects that the evaporator has reached a secondtarget temperature below the freezing point of water, the at least onedamper opens and the evaporator fan starts. In one example, the firsttarget temperature is about 10° C. and the second target temperature isabout −25° C. The controller may also be operable to perform the defrostcycle steps as an adaptive defrost cycle, which includes varying timeperiods between defrost cycles and varying lengths of defrost cyclesdependent upon multiple operating parameters.

In another embodiment of the invention, a method of operating arefrigerator is provided, the refrigerator including a cabinet with arefrigerated interior, a refrigeration fluid circuit including acompressor, a condenser, and an evaporator, and an insulating cover withat least one damper separating the evaporator from the refrigeratedinterior. The method includes stopping operation of the compressor andan evaporator fan. The at least one damper closes to thermally isolatethe evaporator from the refrigerated interior. A defrost heater startsoperation to remove moisture from evaporator coils. The refrigeratedinterior remains thermally isolated from the evaporator during operationof the defrost heater.

In yet another embodiment, a method of operating a refrigerator isprovided, the refrigerator including a cabinet with a refrigeratedinterior, a refrigeration fluid circuit including a compressor, acondenser, and an evaporator, and an insulating cover with at least onedamper separating the evaporator from the refrigerated interior. Themethod includes starting operation of a defrost heater when the at leastone damper is closed. When the evaporator reaches a first targettemperature above the freezing point of water, the defrost heater isstopped and the compressor is started. When the evaporator reaches asecond target temperature below the freezing point of water, the atleast one damper opens and an evaporator fan starts operating.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate an embodiment of the inventionand, together with a general description of the invention given above,and the detailed description of the embodiment given below, serve toexplain the principles of the invention.

FIG. 1 is a perspective view of a refrigerator including an insulatingcover according to an exemplary embodiment.

FIG. 2 is a schematic representation of the refrigeration fluid circuitused with the refrigerator of FIG. 1.

FIG. 3 is a perspective view of the insulating cover (shown in phantom)and dampers used with the refrigerator of FIG. 1.

FIG. 4 is a perspective view of an evaporator used with the refrigeratorof FIG. 1, with some of the side panels shown in phantom to revealinterior elements.

FIG. 5 is a cross-sectional side view of the refrigerator of FIG. 1,with the dampers in a closed position.

FIG. 6 is a cross-sectional side view of the refrigerator of FIG. 5,with the dampers in an open position.

FIG. 7 is a schematic diagram of the controller and damper driveelements used with the refrigerator of FIG. 1.

FIG. 8 is a schematic flowchart illustrating an operational sequence ofa controller associated with the refrigerator of FIG. 1.

DETAILED DESCRIPTION

With reference to the figures, and more specifically to FIG. 1, anexemplary high performance refrigerator 10 according to one embodimentof the present invention is illustrated. Although the terms “highperformance refrigerator” and “refrigerator” are used throughout thespecification, it will be understood that the invention encompasses anytype of cooling device, including a refrigerator that comprises afreezer. The refrigerator of FIG. 1 includes a cabinet 12 for storingitems that require cooling to temperatures of about −30° C. or lower,for example. The cabinet 12 includes a cabinet housing 14 defining agenerally rectangular cross-section and a door 16 providing access intoan interior 18 of the cabinet 12. The cabinet 12 supports one or morecomponents that jointly define a single-stage refrigeration fluidcircuit 20 (FIG. 2) that thermally interacts with the air within thecabinet 12 to cool the interior 18 thereof. In this regard, therefrigeration fluid circuit 20 described in further detail belowinteracts with warmed air in the interior 18 and cools this air tomaintain a desired cold temperature in the cabinet 12.

With reference to FIG. 2, details of the exemplary refrigeration fluidcircuit 20 are illustrated. The refrigeration fluid circuit 20 includes,in sequence, a compressor 22, a condenser 24, a filter/dryer 26, anexpansion device 28, an evaporator 30, and a suction/accumulator 32.Each of these elements of the refrigeration fluid circuit 20 is coupledby piping or tubing 34 configured to circulate the refrigerant 36passing through the refrigeration fluid circuit 20. A plurality ofsensors S₁ through S₅ are arranged to sense different conditions of thefluid circuit 20 and/or properties of the refrigerant (shown by arrows36) at various locations within the fluid circuit 20. Each of thesesensors S₁ through S₅ is operatively coupled to a controller 50accessible through a controller interface 52, which permits controllingof the operation of the fluid circuit 20. It will be appreciated thatmore or fewer sensors may be provided than the number shown in theexemplary embodiment of the fluid circuit 20.

The refrigeration fluid circuit 20 is configured to circulate therefrigerant 36 between the condenser 24 and the evaporator 30. Generallyspeaking, heat energy in the refrigerant 36 is transferred to ambientair outside the cabinet 12 at the condenser 24. Heat energy is removedfrom the interior 18 of the cabinet 12 and transferred to therefrigerant 36 at the evaporator 30. Thus, circulating the refrigerant36 through the fluid circuit 20 continuously removes heat energy fromthe interior 18 to maintain a desired internal temperature, such as, forexample −30° C.

The refrigerant 36 enters the compressor 22 in a vaporized state and iscompressed to a higher pressure and higher temperature gas in thecompressor 22. The fluid circuit 20 of this exemplary embodiment alsoincludes an oil loop 54 for lubricating the compressor 22. Specifically,the oil loop 54 includes an oil separator 56 in fluid communication withpiping 34 downstream of the compressor 22 and an oil return line 58directing oil back into the compressor 22. It will be understood thatthe oil loop 54 may be omitted in some embodiments of the fluid circuit20.

Upon leaving the compressor 22, the vaporized refrigerant 36 travels tothe condenser 24. A fan 60 controlled by the control interface 52directs ambient air across the condenser 24 and through a filter 62 soas to facilitate the transfer of heat from the refrigerant 36 to thesurrounding environment. The air flow through the condenser 24 is shownby arrows in FIG. 2. The refrigerant 36 condenses within the condenser24 as a result of this heat transfer. The liquid-phase refrigerant thenpasses through the filter/dryer 26 and into the expansion device 28. Inthis embodiment, the expansion device 28 is in the form of a capillarytube, although it is contemplated that it could instead take anotherform such as, and without limitation, an expansion valve (not shown).The expansion device 28 causes a pressure drop in the refrigerant 36immediately before the refrigerant 36 enters the evaporator 30.

In the evaporator 30, the refrigerant 36 receives heat from the interior18 through a plurality of evaporator coils (not shown in FIG. 2). Anevaporator fan 64 controlled by the control interface 52 forces air flowfrom the interior 18 of the cabinet 12 through the evaporator coils whenfirst and second dampers 66, 68 are opened. The first and second dampers66, 68 are also controlled by the control interface 52. The control ofthe first and second dampers 66, 68 is further described with referenceto FIG. 8, below. By virtue of the lowered pressure and the heattransfer from the cabinet 12, the refrigerant 36 vaporizes within theevaporator 30. The vaporized refrigerant 36 is then directed to thesuction/accumulator device 32. The suction/accumulator 32 passes therefrigerant 36 in gaseous form to the compressor 22, while alsoaccumulating excessive amounts of the refrigerant 36 in liquid form andfeeding it to the compressor 22 at a controlled rate.

The refrigerant 36 used in the refrigeration fluid circuit 20 may bechosen based on several factors, including the expected operatingtemperature within the cabinet 12 and the boiling point and othercharacteristics of the refrigerant 36. For example, in refrigeratorswith an expected cabinet temperature of about −30° C., an exemplaryrefrigerant 36 suitable for the presently described embodiment includesrefrigerants commercially available under the respective designationsR404A. Moreover, in specific embodiments, the refrigerant 36 may becombined with an oil to facilitate lubrication of the compressor 22. Forexample, and without limitation, the refrigerant 36 may be combined withMobil EAL Arctic 32 oil. It will be understood that the precisearrangement of the components illustrated in the figures is intended tobe merely exemplary rather than limiting.

With reference to FIGS. 3-6 and in particular FIG. 3, the refrigerator10 includes an insulated cover 70 that divides the interior 18 of thecabinet 12 into an evaporator portion 72 and a refrigerated portion 74.The insulated cover 70 is coupled to one or more of the top wall 76, theside walls 78 (including a rear wall 78), and/or the bottom wall 80collectively defining the cabinet housing 14. More particularly, theinsulated cover 70 is coupled to the top wall 76 and the side walls 78of the cabinet housing 14 to thermally isolate the evaporator portion 72from the heat energy within the interior 18 as that heat energy riseswithin the interior 18 of the cabinet 12. The insulated cover 70 of theillustrated embodiment includes a vertical panel portion 82 extendingdownwardly from the top wall 76 of the cabinet housing 14 and ahorizontal panel portion 84 extending between the vertical panel portion82 and the side walls 78 of the cabinet housing 14. The vertical panelportion 82 and the horizontal panel portion 84 are formed from one ormore thermally insulating panels, such as the hollow vacuum insulatedpanel 86 shown in FIG. 3. It will be understood that other types ofinsulating panels may be used in other embodiments of the invention,including but not limited to foam-based panels.

As shown in FIG. 3, the evaporator portion 72 is defined as a generallyrectilinear space by the vertical panel portion 82, the horizontal panelportion 84, the side walls 78, and the top wall 76. The evaporator 30mounts into a divider panel 88 located generally centrally within theevaporator portion 72 so as to divide the evaporator portion 72 into aninlet side 90 and an outlet side 92. The divider panel 88 is anothervacuum insulated panel or foam-based insulated panel in this embodiment,although it will be understood that other types of dividing panels mayalso be used in other embodiments. The horizontal panel portion 82 ofthe insulated cover 70 includes an inlet aperture 94 on the inlet side90 of the divider panel 88 and an outlet aperture 96 on the outlet side92 of the divider panel 88. The first damper 66 includes an insulatedpanel that is operable to rotate to open or close flow through the inletaperture 94 between the inlet side 90 and the refrigerated interior 18of the cabinet 12. Similarly, the second damper 68 includes an insulatedpanel that is operable to rotate to open or close flow through theoutlet aperture 96 between the outlet side 92 and the refrigeratedinterior 18 of the cabinet 12. Thus, the first and second dampers 66, 68may be operated to enable flow through the evaporator 30.

Also shown in FIG. 3, the first and second dampers 66, 68 areoperatively connected to a damper drive mechanism 100 such as respectivefirst and second servo motors 102, 104 and first and second drive shafts106, 108. The control and operation of the damper drive mechanism 100 isfurther described in detail with reference to FIG. 7 below. It will beunderstood that the first and second drive shafts 106, 108 may beconnected by a conventional drive linkage (not shown) in someembodiments so that only a single servo motor would be required to openand close the first and second dampers 66, 68. In this regard, the firstand second dampers 66, 68 are typically opened (or closed)simultaneously so that flow is enabled through the evaporator portion 72and the evaporator 30.

Turning to FIG. 4, the evaporator 30 is shown in further detail. To thisend, the evaporator 30 includes an evaporator housing 110 enclosing anevaporator coil 112 extending in a serpentine manner across a width ofthe evaporator 30. The evaporator coil 112 is operatively connected tothe piping 34 of the refrigeration fluid circuit 20, which carriesliquid-phase refrigerant to the evaporator coil 112 and removesvaporized and any remaining liquid-phase refrigerant from the evaporatorcoil 112. The evaporator fan 64 is mounted along the evaporator housing110 at the inlet side 90 of the evaporator portion 72 so as to actuateair flow through the evaporator housing 110 and through the evaporatorcoil 112. After flowing through the evaporator coil 112, cooled airexits the evaporator housing 110 and enters the outlet side 92 of theevaporator portion 72.

The evaporator 30 also includes a defrost heater 114 for removing frostbuild up on the evaporator coil 112 as needed or on a regular basis. Thedefrost heater 114 is shown mounted adjacent to the evaporator coil 112in FIGS. 4 and 5, but it will be appreciated that the defrost heater 114may be mounted anywhere within the evaporator housing 110. The defrostheater 114 is operated by the controller 50 and the control interface 52previously described with reference to FIG. 2 to heat up the evaporatorcoil 112 and melt any frost. The evaporator housing 110 further includesa drip pan 116 located below the evaporator coil 112 and configured tocollect and dispose of melted frost to a location outside therefrigerator 10. In this regard, the drip pan 116 is generally angledfrom a horizontal orientation so that moisture dripping from theevaporator coil 112 automatically flows to a moisture outlet (notshown).

With reference to FIGS. 5 and 6, the refrigerator 10 further includes anupper compartment 120 located above the top wall 76 of the cabinethousing 14. The upper compartment 120 contains elements of therefrigeration fluid circuit 20 other than the evaporator 30 (e.g., thecompressor 22, the condenser 24, etc.), thereby removing most of thespace-using or heat generating components from the interior 18 of thecabinet 12. These other elements located within the upper compartment120 are not shown in FIGS. 5 and 6, although they are schematicallyshown in FIG. 2. The piping 34 for the refrigerant 36 extends throughthe top wall 76 to deliver refrigerant between the components in theupper compartment 120 and the evaporator 30 in the cabinet 12.

FIGS. 5 and 6 also illustrate two operating states for the refrigerator10. More particularly, in FIG. 5 the first and second dampers 66, 68 areclosed, which thermally isolates the evaporator portion 72 from therefrigerated portion 74. The evaporator fan 64 is generally inactivewhen the first and second dampers 66, 68 are closed because air cannotbe circulated into and out of the evaporator portion 72. The defrostheater 114 is only operated in this operational state of therefrigerator 10 so that substantially all of the heat energy generatedby the defrost heater 114 remains within the evaporator portion 72during a defrost cycle or process. To this end, the temperature spikewithin the refrigerated portion 74 of the interior 18 is reduced oreliminated during the defrost cycle. In contrast, the first and seconddampers 66, 68 are open in FIG. 6 so that air from the refrigeratedportion 74 may flow through the evaporator 30 and the evaporator coil112 for cooling. The air flow actuated by the evaporator fan 64 isschematically shown in FIG. 6 by arrows 122. Thus, relatively warm airenters the evaporator portion 72 through the inlet aperture 94 andrelatively cold air exits the evaporator portion 72 through the outletaperture 96 in this operating state of the refrigerator 10.

FIG. 7 schematically illustrates the control and actuation mechanismsfor the first and second dampers 66, 68. More specifically, the firstand second dampers 66, 68 are connected to the damper drive mechanism100, which is coupled to the controller 50. As understood in the art,the controller 50 may include at least one central processing unit(“CPU”) coupled to a memory. Each CPU is typically implemented inhardware using circuit logic disposed on one or more physical integratedcircuit devices or chips. Each CPU may be one or more microprocessors,micro-controllers, field programmable gate arrays, or ASICs, whilememory may include random access memory (RAM), dynamic random accessmemory (DRAM), static random access memory (SRAM), flash memory, and/oranother digital storage medium, and also typically implemented usingcircuit logic disposed on one or more physical integrated circuitdevices, or chips. As such, memory may be considered to include memorystorage physically located elsewhere in the refrigerator 10, e.g., anycache memory in the at least one CPU, as well as any storage capacityused as a virtual memory, e.g., as stored on a mass storage device suchas a hard disk drive, another computing system, a network storage device(e.g., a tape drive), or another network device coupled to thecontroller 50 through at least one network interface by way of at leastone network. The computing system, in specific embodiments, is acomputer, computer system, computing device, server, disk array, orprogrammable device such as a multi-user computer, a single-usercomputer, a handheld computing device, a networked device (including acomputer in a cluster configuration), a mobile telecommunicationsdevice, a video game console (or other gaming system), etc. Thecontroller 50 includes at least one serial interface to communicateserially with an external device, such as the damper drive mechanism100, for example. Thus, the controller 50 functions to actuate operationof the damper drive mechanism 100.

As previously described, the damper drive mechanism 100 may be one ormore servo motors 102, 104 connected to the first and second dampers 66,68 via corresponding drive shafts 106, 108. However, the damper drivemechanism 100 may include other types of actuation mechanisms anddevices in other embodiments. For example, the damper drive mechanism100 may be hydraulically driven, pneumatically driven, or mechanicallydriven such as by various types of motors. The damper drive mechanism100 may be configured to rotate the dampers 66, 68 between open andclosed positions as shown in the illustrated embodiment, but it will beunderstood that the damper drive mechanism 100 may alternatively slideor otherwise move the dampers 66, 68 in non-rotational manners as well.

An exemplary operation of the refrigerator 10 is shown schematically inthe flowchart of FIG. 8. In this regard, the controller 50 is operableto command the refrigerator 10 to execute the steps of the method 200shown in that Figure. To this end, the controller 50 determines whethera defrost cycle is necessary at step 202. For example, in a time-baseddefrost cycle, the controller 50 at step 202 determines whether apredetermined amount of time has elapsed since the most recent defrostcycle. If so, then the controller 50 begins the defrost cycle at step204. If not, then the controller 50 continues to wait and periodicallychecks to see if the predetermined amount of time has elapsed. In oneexample, the refrigerator 10 may defrost every six hours, in which casethe predetermined amount of time would be six hours. Alternatively, thecontroller 50 may be operable to perform adaptive defrosts that arespaced by varying amounts of time depending on operationalcharacteristics measured between defrost cycles, as described in furtherdetail below.

Returning to FIG. 8, when a defrost cycle is required to remove frostbuild up from the evaporator coil 112, the controller 50 stops thecompressor 22 and the evaporator fan 64 at step 204. This stopsrefrigerant flow through the refrigeration fluid circuit 20 and theevaporator 30 and also stops air flow through the evaporator 30. Thecontroller 50 then closes the first and second dampers 66, 68 at step206 to thermally isolate the evaporator portion 72 from the refrigeratedportion 74 of the cabinet 12. With the evaporator portion 72 thermallyisolated from the remainder of the cabinet 12, the controller 50 startsoperation of the defrost heater 114 at step 208. The defrost heater 114warms the evaporator 30 and the evaporator coil 112 to melt frost andcause the moisture to drip onto the drip pan 116 for removal from theevaporator 30. The operational state of the refrigerator 10 at thispoint is shown in FIG. 5.

One of the sensors S₃ connected to the evaporator 30 may be configuredto measure the temperature of the evaporator 30. At step 210, thecontroller 50 determines whether that sensor S₃ is reading a temperatureof the evaporator 30 which is at or exceeding a first target temperatureabove the freezing point of water (0° C.). In one example, this firsttarget temperature may be about 10° C. If the evaporator 30 is not at orabove that first target temperature, then the controller 50 continues tooperate the defrost heater 114 to remove frost from the evaporator coil112. If the evaporator 30 is at or above the first target temperature,then the controller 50 turns off the defrost heater 114 and allows a setperiod of time for additional moisture to drip off the evaporator coil112 onto the drip pan 116 at step 212. After this “drip time” hasoccurred, the controller 50 starts the compressor 22 to causerefrigerant flow through the evaporator 30 again at step 214, therebycooling the evaporator portion 72.

At step 216, the temperature sensor S₃ measures the temperature of theevaporator 30 and the controller 50 determines whether this temperatureis at or below a second target temperature below the freezing point ofwater (0° C.). In one example, this second target temperature may beabout −25° C. If the evaporator 30 is not at or below the second targettemperature, the controller 50 continues to operate the compressor 214to cool the evaporator 30. Once the controller 50 determines that theevaporator 30 is at or below the second target temperature, then thecontroller 50 opens the first and second dampers 66, 68 at step 218. Thecontroller 50 also starts the evaporator fan 64 at step 220, to therebyforce air flow from the refrigerated portion 74 through the evaporatorportion 72 and the evaporator 30 for further cooling. This final step ofthe defrost cycle or method 200 returns the refrigerator 10 to theoperational state shown in FIG. 6, which is the normal coolingoperational state. As a result of the insulated cover 70, the defrostcycle does not cause a significant temperature spike within therefrigerated interior 18 of the cabinet 12, and the refrigerator 10therefore is advantageous over conventional refrigerator designs.

As briefly noted above, in one alternative embodiment the defrost cyclewill be an adaptive defrost cycle selectively actuated at step 202 ofthe method 200. In this adaptive defrost cycle, the period betweendefrost cycles and the time duration of the defrost cycles are modifiedbased on a plurality of operational parameters monitored by thecontroller 50. For example, the conventional time-based defrost cyclemay operate the defrost heater 114 for 10 minutes every six hours. Bycontrast, the adaptive defrost cycle may monitor the actual temperaturebeing maintained in the cabinet 12, as well as the number of dooropenings and amount of total time the door is open. These and otherfactors are considered to determine how long the period should be beforethe next defrost cycle is started, and also how long the defrost heater114 should be operated in the next defrost cycle. In this regard, if thedoor of the cabinet 12 is not opened often during a six hour period andthe evaporator 30 is having little trouble maintaining the desiredtemperature within the refrigerated portion 74, then the next defrostcycle may be delayed by an additional number of hours and/or shortenedin duration. Thus, the adaptive defrost cycle is highly energy efficientbecause the evaporator coil 112 is only defrosted when that cyclebecomes necessary. Moreover, the adaptive defrost cycle automaticallyadjusts the refrigerator 10 for proper and efficient operation in avariety of environmental conditions.

While the present invention has been illustrated by a description of anexemplary embodiment and while this embodiment has been described inconsiderable detail, it is not the intention of the applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. The invention in its broader aspects istherefore not limited to the specific details, representative apparatusand method, and illustrative example shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of applicant's general inventive concept.

What is claimed is:
 1. A refrigerator, comprising: a cabinet having arefrigerated interior; a refrigeration fluid circuit for circulating arefrigerant, the refrigeration fluid circuit including a compressor, acondenser, an expansion device, and an evaporator located within thecabinet and including an evaporator coil, an evaporator fan producingair flow through the evaporator coil, and a defrost heater; aninsulating cover separating a portion of the cabinet containing theevaporator from the refrigerated interior, the insulating coverincluding at least one damper that may open to permit air circulationfrom the refrigerated interior through the evaporator; and a controlleroperable to command the refrigerator to perform the following steps whenthe evaporator coil requires defrosting: stop operation of thecompressor and the evaporator fan; close the at least one damper tothermally isolate the evaporator from the refrigerated interior; andstart operation of the defrost heater, wherein the refrigerated interiorremains thermally isolated from the evaporator during operation of thedefrost heater.
 2. The refrigerator of claim 1, further comprising atemperature sensor for detecting the temperature of the evaporator, andwherein the controller is further operable to command the refrigeratorto perform the following steps during defrosting of the evaporator: whenthe temperature sensor detects that the evaporator has reached a firsttarget temperature above the freezing point of water, stopping operationof the defrost heater and allowing for any remaining moisture to dripoff the evaporator coils; starting the compressor after the remainingmoisture drips off the evaporator coils; and when the temperature sensordetects that the evaporator has reached a second target temperaturebelow the freezing point of water, opening the at least one damper andstarting operation of the evaporator fan.
 3. The refrigerator of claim2, wherein the first target temperature is about 10° C. and the secondtarget temperature is about −25° C.
 4. The refrigerator of claim 1,wherein the at least one damper includes a first damper and a seconddamper, the first damper in an open position permitting air flow intothe evaporator from the refrigerated interior, the second damper in anopen position permitting air flow from the evaporator into therefrigerated interior.
 5. The refrigerator of claim 1, wherein theinsulated cover further includes a plurality of insulated panels thatcollectively divide the cabinet into an evaporator chamber and therefrigerated interior when the at least one damper is closed.
 6. Therefrigerator of claim 5, wherein each of the insulated panels is avacuum insulated panel.
 7. The refrigerator of claim 1, wherein theexpansion device includes at least one of a capillary tube or a valve.8. The refrigerator of claim 1, wherein the refrigeration fluid circuitfurther includes an accumulator operatively connected to the evaporatorand the compressor.
 9. The refrigerator of claim 1, wherein therefrigeration fluid circuit further includes a filter/dryer operativelyconnected to the condenser and the expansion device.
 10. Therefrigerator of claim 1, wherein the controller is operable to modify anamount of time between defrost cycles and to modify an amount of timethe defrost heater is operating during a defrost cycle based on at leastone measurable operating parameter.
 11. A method of operating arefrigerator including a cabinet having a refrigerated interior, arefrigeration fluid circuit including a compressor, a condenser, and anevaporator located within the cabinet and having an evaporator fan anddefrost heater, the refrigerator further including an insulating coverwith at least one damper configured to separate the evaporator from therefrigerated interior of the cabinet, and the method comprises: stoppingoperation of the compressor and the evaporator fan; closing the at leastone damper to thermally isolate the evaporator from the refrigeratedinterior; and starting operation of the defrost heater, wherein therefrigerated interior remains thermally isolated from the evaporatorduring operation of the defrost heater.
 12. The method of claim 11,further comprising: when the evaporator has reached a first targettemperature above the freezing point of water, stopping operation of thedefrost heater and allowing for any remaining moisture to drip off theevaporator coils; starting the compressor after the remaining moisturedrips off the evaporator coils; and when the evaporator has reached asecond target temperature below the freezing point of water, opening theat least one damper and starting operation of the evaporator fan. 13.The method of claim 12, wherein the first target temperature is about10° C. and the second target temperature is about −25° C.
 14. The methodof claim 11, wherein the at least one damper includes a first damper anda second damper, the first damper in an open position permitting airflow into the evaporator from the refrigerated interior, the seconddamper in an open position permitting air flow from the evaporator intothe refrigerated interior, and the first and second dampers aresimultaneously closed by the refrigerator when the operation of theevaporator fan is stopped.
 15. A method of operating a refrigeratorincluding a cabinet having a refrigerated interior, a refrigerationfluid circuit including a compressor, a condenser, and an evaporatorlocated within the cabinet and having an evaporator fan and defrostheater, the refrigerator further including an insulating cover with atleast one damper configured to separate the evaporator from therefrigerated interior of the cabinet, and the method comprises: startingthe operation of the defrost heater when the at least one damper isclosed; and when the evaporator has reached a first target temperatureabove the freezing point of water, stopping operation of the defrostheater and starting operation of the compressor; and when the evaporatorhas reached a second target temperature below the freezing point ofwater, opening the at least one damper and starting operation of theevaporator fan.
 16. The method of claim 15, wherein the first targettemperature is about 10° C. and the second target temperature is about−25° C.
 17. The method of claim 15, wherein the at least one damperincludes a first damper and a second damper, the first damper in an openposition permitting air flow into the evaporator from the refrigeratedinterior, the second damper in an open position permitting air flow fromthe evaporator into the refrigerated interior, and the first and seconddampers are simultaneously opened by the refrigerator when the operationof the evaporator fan is started.